Blue discolouration in a neuroischaemic foot

A 48-year-old man with type 1 diabetes mellitus of 20 years' duration, peripheral neuropathy, background retinopathy and no proteinuria presented with a 1-week history of malaise, high blood glucose and a 2-day history of discomfort and redness of the right foot. There was no history of trauma. There was an area of erythema over the dorsum and both medial and lateral aspects of the right foot, which was also oedematous. There was no break in the skin (Fig. 5.20a).

Body temperature was 39.2°C, pulse 104 regular, foot pulses absent, chest clear, abdomen normal. Haemoglobin 11.4 g/dL, WBC 17.3 109/L, erythrocyte sedimentation rate (ESR) 105, HbA, 13% and glucose 18.6mmol/L (335 mg/dL). X-ray of the foot was normal. Blood cultures showed no growth. There was no open lesion to take a swab.

Doppler studies in both legs showed a very high ankle/ brachial pressure index (above 1.5) indicative of calcification. The foot artery waveforms were damped, indicating reduced blood flow. A clinical diagnosis of cellulitis in a neuroischaemic foot was made. The other much less likely diagnosis was an acute onset of Charcot's osteoarthropathy. However, it is unusual for Charcot's osteoarthropathy to be associated with such a high body temperature, which is much more suggestive of sepsis.

He was treated with quadruple intravenous antibiotic therapy (amoxicillin 500 mg tds, flucloxacillin 500 mg qds, metronidazole 500 mg tds and ceftazidime 1 g tds) to provide a wide spectrum cover and commenced on sliding scale intravenous insulin. By the next day, body temperature had fallen to 37.2°C but there was no improvement in the cellulitis. There were spikes of fever on the evening of the second and third days (Fig. 5.20b). The area of cellulitis did not regress, but there was no evidence of a collection of pus. A surgical opinion was obtained and confirmed that there was no indication for surgery.

On the fourth day of the admission the patient was still pyrexial. He also had a rigor. The ceftazidime was withdrawn and intravenous gentamicin 80 mgtds started. (This was before once-daily dosaging had come in.) The most common organism isolated in diabetic foot infections is Staphylococcus aureus and gentamicin is active against Staphylococcus as well as providing Gram-negative cover.

Staphylococcus Aureus Foot

Fig. 5.20 (a) Area of redness and oedema on the medial border of the foot at presentation, (b) The temperature chart shows spikes of fever over the first 5 days with resolution of fever after surgery, (c) A patch of purplish discolouration has appeared

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